1. Field of the Invention
The present invention pertains to improved fluids known in the oil service industry as drilling fluids or muds, and, in particular, to invert emulsion types of drilling fluids in which water is dispersed in an oil-based medium. The invention is particularly directed to providing enhanced anti-settling properties to such drilling fluids; that is, the invention enhances the ability of such fluids to retain in suspension, and to convey along with the fluid, a variety of types of solid particles.
The invention discloses new drilling fluids, which are distinguished by improved anti-settling properties, high ecological acceptability, and at the same time good storage and application properties.
An important area of application for the new disclosed drilling fluids is in both on- and off-shore wells for the development of hydrocarbon deposits, the aim of the invention being particularly to make available industrially--usable drilling fluids with enhanced anti-settling properties. The new drilling fluid systems can also be used in land-based drilling operations beyond those for oil and hydrocarbons.
2. Description of the Prior Art
Anti-settling Properties of Drilling Fluids
Early oil well drilling was done with hammer bits. Shortly after the beginning of United States commercial oil drilling operations in Pennsylvania and Ohio, the oil industry introduced motor-driven rotary drilling bits which used "drilling muds" or drilling fluids along with the motor-driven bits. Drilling fluids have been much the subject of development over the subsequent years which development continues to date.
Drilling fluids, in their almost infinite variety, today must be pumpable under pressure down through strings of drilling pipe, then through and around the drilling bit head deep in the earth, and then returned back to the earth surface through an annulus between the outside of the drill stem and the hole wall or casing. A casing over the natural hole wall surface is sometimes installed while the hole is being drilled to target depth.
Drilling base muds, the liquid carriers of the system, are often comprised of oils (diesel, mineral, and poly(alpha-olefin)), propylene glycol, methyl glucoside, modified esters and ethers, water, and emulsions of oil and water of varying proportions.
Beyond providing drilling lubrication and efficiency, and retarding wear, drilling fluids must accomplish a number of important interrelated functions falling under the term, "anti-settling" for these fluids to satisfy the minimum requirements for commercial drilling fluids. These functions can be grouped as follows:
(1) The fluid must suspend and transport solid particles to the surface for screening out and disposal,
(2) The fluid must suspend additive weighting agents (to increase specific gravity of the mud), generally finely ground barytes (barium sulfate ore), and
(3) The fluid must transport clay and other substances capable of adhering to and coating the borehold surface, both to exclude unwanted fluids which may be encountered, such as brines, preventing them from mixing with and degrading the rheological profile of the drilling mud, and to prevent the loss of downhole pressure from fluid loss into porous formations.
The interrelatedness of these anti-settling functions can be seen by the fact that unwanted materials to be removed at the surface can include not only "cuttings" from the material through which the bit is passing, but also broken pieces of the drill bit itself, spent barytes or other weighting materials, and substances such as gellants and salts created when other fluid constituents become "spent" through harsh drilling conditions such as reaction processes under the temperatures encountered in deeper wells. Thus, substances added to achieve a desirable property, such as improved lubrication or pressure control, potentially result in the ultimate creation of a waste to be removed by the drilling fluid. In addition, every reformulation of a drilling fluid potentially alters the physical characteristics of the fluid in a way that inhibits the removal of unwanted ingredients.
Drilling fluids are thixotropic systems. That is, (1) they exhibit low viscosity when sheared, such as when in circulation (as by pumping or otherwise) but, (2) when the shearing action is halted, the fluid sets or gels to hold the solids it contains in place. The fluid must become gelled relatively rapidly, reaching a sufficient gel strength before suspended materials fall downward any significant distance. This gellation behavior must be totally reversible.
In addition, even when the drilling fluid is a free-flowing near-liquid, it must retain a sufficiently high enough viscosity to carry all unwanted particulate matter from the bottom of the often deep hole to the surface. While not used in highly environmentally sensitive areas, upon long-term interruption of circulation when drilling fluid must be ejected from the borehole and placed into a holding area near the bore hole, the drilling fluid gel structure must also be such as to allow the cuttings and other unwanted particulates to settle out from the liquid fraction over time.
Drilling muds and their compositions have over the years involved the attention of both scientists and artisans, with thousands of various improvements made and patented. One of the principal problems facing "mud chemistry" scientists and technicians is the production of drilling fluids having satisfactory dispersibility, with the necessary subsidiary thixotropic properties discussed above, while at the same time possessing the above-described critically important anti-settling properties. Fluids and their additives involve highly complex chemical, physical and rheological analysis using state-of-the-art scientific apparatus and intricate mathematical calculations and modeling.
"Anti-settling" involves considerations of assurance of suspension and control of widely-varying matter covered under the general rubric "cuttings." It entails a different measure of control when shear rate and force is high, low, or non-existent, and requires control of syneresis and deposition of such particles over wide ranges of a) temperature (from 0.degree. to as high as 300.degree. C.), b) time durations, c) pressures (from only a few bars to those exerted by a column of fluid that can extend for thousands of feet) and d) drilling directions (from vertical to horizontal).
A search has been going on for many years for an improved additive for modifying and controlling the suspension properties of drilling fluids that will provide fluids which are efficient, easily handled, and readily dispersible, and usable under a broad range of conditions.
Drilling Muds/Oil-Based Invert Emulsion Drilling Fluids
Drilling fluids or muds are typically classified according to their base fluid or continuous phase, as "water-base muds" and "oil-base muds". Drilling muds may contain a mixture of base fluids, and are typically classified by the predominating or continuous base fluid, with the fluid present in lesser quantities becoming the internal or emulsified phase.
Another class of drilling muds, in addition to water-based muds and oil-based muds, are pneumatic muds, in which drill cuttings are removed by a high velocity stream of air or another gas, including natural gas.
Oil-base muds, for example, may have an aromatic or aliphatic oil, or a mixture of oils, as the continuous phase. These oils may include diesel, mineral or synthetic (PAO, esters, ether) oil. They may be comprised entirely of oil or, more commonly, may contain water ranging from 5% to upwards of 50-60%. In this mud, water becomes the internal phase, is emulsified into the oil as a heterogeneous fine dispersion, and the resulting system is referred to as an oil-based or oil-invert emulsion mud.
The invention hereof is particularly useful for oil-based invert emulsion drilling fluids. These fluids are generally used in the United States, and elsewhere such as in the North Sea, and consist of a three-phase system: oil, water, and fine particulate solids. The aqueous phase may be a brine. The addition of brine reduces the overall price of the fluid, reduces the risk of combustion of the oil, and improves the water acceptance of the mud. The brine of choice is commonly an aqueous solution of an inorganic salt such as sodium chloride or calcium chloride.
Drilling on Land and Off-Shore
Hydrocarbon drilling for exploratory (and production) wells has long been done on land. In the last 30 to 40 years, such drilling has been done from platforms located in water settings; so-called off-shore drilling. Shallow fresh and salt water drilling operations generally employ different equipment than deeper water operations. Shallow fresh or salt water drilling operations most often use barges or fixed rigs while deep water off-shore operations employ jack-ups, semi-submersibles, and floating drillship rigs.
In off shore drilling, drill cuttings removed from the bore-hole must either be discharged to the surrounding body of land or water, or transported to a remote location; the liquid phase of spent drilling fluids must similarly be disposed of. The disposal of cuttings may be inhibited by the presence of harmful substances adhering to cuttings particles, whether oil from the fluid or a material encountered in the borehole.
The use of oil-based invert emulsion drilling fluids or muds in oil exploration has been increasing rapidly over the last twenty years owing to the more demanding requirements encountered in drilling deep and/or non-vertical and deviated wells. Compared with the longer-established oil and water based muds including diesel and mineral oil based muds, such invert oil based drilling muds possess a number of advantages, including reduced interaction with earth formations, greater thermal stability and improved lubricity.
The drilling fluids and methods of this invention are particularly useful for oil-based invert emulsion drilling fluid systems.
Directional Drilling and the New Problems as to Settling that it Causes
The requirements for drilling muds as they relate to anti-settling properties have also become even more complex as a result of the introduction over the last 20 years of directional drilling technology, in which at least a portion of the well is drilled at an angle other than vertical. Such wells are also known as deviated wells.
Procedures for deviating wells have improved greatly over recent years with the introduction of more powerful and reliable downhole motors, and the introduction of more accurate interpretation of wireline data as well as utilization of the latest computerized downhole and sensing equipment, including improvements in sound and microwave transmissions. These techniques are collectively referred to as Measurement While Drilling (MWD) techniques, because they permit the obtaining of data relating to down-hole conditions without the need to remove the drill string.
The advantages of directional drilling are becoming well-known: such drilling permits (1) the salvaging of boreholes blocked by debris (such as tools which have become inextricably lodged); (2) the use of more economical land-based equipment to explore the immediate off-shore environment; and (3) the drilling of multiple wells up to several miles from one another, sharing the cost of a single platform. In certain formations, increased production can be achieved by deviating the well off-vertical so as to facilitate perforation and development of a narrow producing zone, or redevelopment of a depleted formation.
There are, however, a number of inherent problems in this approach to directional drilling, which affect the anti-settling requirements or sag properties as referred to in the drilling industry, of a drilling mud; namely:
(1) The amount of drilling mud required is increased, since the distances are greater, and the time required for the cuttings to reach the earth's surface also increases.
(2) The annulus carrying the mud with cuttings to the surface is no longer vertical and gravity on a horizontal hole pulls cuttings, weighting material and particulate matter, not controlled by the drilling fluid, to the lower side of the bore rather than the bottom of the hole.
Work In The Past
There are a large number of prior art patents relating to drilling fluids. The below is not intended to be an exhaustive summary.
U.S. Pat. No. 4,486,316 shows a drilling fluid comprising an aqueous dispersion of an emulsion polymerized latex comprised of an interpolymer of an olefinically unsaturated carboxylic acid monomer and at least one other, non-carboxylated polymerizable monomer, the latex being of a type which undergoes rapid increase in viscosity upon the addition of a sufficient amount of a basic material. U.S. Pat. No. 2,999,063 describes adding a mixture of a particular class of amine and metallic soap to a mixture of water in oil and describes that the mixture provides emulsion properties to drilling and packing fluids. U.S. Pat. No. 4,374,737 relates to a drilling mud composition having non-polluting, non-diesel fuel-based properties. The invention is directed to a non-polluting additive for improving the rheological properties of drilling muds consisting of the following ingredients: a diethanolamide of a specific formula, tall oil fatty acid and an imidazoline/amide mixture consisting essentially of three specifically defined chemicals.
U.S. Pat. No. 5,254,531 describes oleophilic basic amine additives for invert drilling muds to regulate the flowability and pumpability of the drilling mud. The patent describes adding to the mud, containing an esterified oil, a basic amine compound having an oleophilic character and limited solubility in water and thereby forming in situ in the drilling mud an oil-soluble salt with said amine compound and a carboxylic acid formed by hydrolysis of the ester. U.S. Pat. No. 3,879,298 shows a method of controlling the rheology of a fresh water drilling fluid contaminated with salt by incorporating therein an ethylenedicarboxylic acid additive. The additive may comprise maleic acid, maleic acid anhydride, and mixtures thereof
U.S. Pat. No. 4,781,730 describes an alkali metal or alkaline earth metal-containing composition (with or without a hydrocarbon-soluble dispersant) which is combined with the reaction product of a carboxylic acid and a polyhydroxyalkanolamine, with the preferred reaction product being an ester which forms between the hydroxyl moieties of the alkanolamine and the carboxylic acid (anhydride). The reaction product of the carboxylic acid and polyhydroxyalkanolamine acts as a demulsifier for the alkali metal or alkaline earth metal-containing composition. The patent describes a composition comprising a hydrocarbon-soluble or dispersible alkali metal or alkaline earth metal containing composition, and the reaction product of a polybasic acid and a polyhydroxyalkanolamine of the formula RN[(AO).sub.x H][(DO).sub.y H]. The polybasic acid may be either an acid or an anhydride, and is preferably a dicarboxylic acid.
Several prior art patents disclose chemistry and chemical reactions which may be of interest.
Japanese Patent Application No. 62-69957 describes a sag preventer for non-aqueous coatings comprising a mixture of two different fatty acid amides wherein fatty acid amide (A) is obtained by reacting a mixture of at least one straight chain saturated fatty acid having 3-4 carbon atoms and 12-hydroxystearic acid (the molar ratio of the fatty acid and 12-hydroxystearic acid being 1:9-8:1) and ethylene diamine or hexamethylene diamine and fatty acid amide (B) is obtained by reacting a mixture of at least one straight chain saturated fatty acid having 6-22 carbon atoms and 12-hydroxystearic acid (the molar ratio of the fatty acid and 12-hydroxystearic acid being 0:10-8:2) and ethylene diamine or hexamethylene diamine, wherein the weight ratio of fatty acid amide (A) to fatty acid amide (B) is 100:00-20:80.
U.S. Pat. No. 5,374,687, issued to the assignee hereof, discloses a paint additive for water-reducible paints which is a low molecular weight reaction product of an alpha-olefin and an alpha, beta-ethylenically unsaturated carboxylic acid. See also U.K. Patent No. 1,268,418 showing dispersion aids for resinous plastics using similar copolymers.